自組性單層薄膜（self assembled monolayer, SAM）因可使基材表面達到功能化之目的，已成為生物感測等領域相繼使用的表面改質技術。由於SAM的修飾會改變電極表面的阻抗，故研究中擬以電阻抗分析評估SAM的特性，且以SAM固定白蛋白（avidin）作為生物素（biotin）之感測探針，由量測avidin-biotin鍵結產生的阻抗，達到檢測biotin之目的。
　　
　　實驗中，分別將三種硫醇分子（DTBA、MUA與MHA），修飾在金電極表面，且另一端之官能基分子均為COOH。接著將SAM之COOH官能基以EDC/NHS活化，使avidin固定在金電極表面，作為檢測biotin之探針。電路模型的建立為比較DTBA、MUA及MHA於電極表面所得之阻抗響應，進而確立電路模型中各元件所代表之物理意義。由結果可知，電路模型中的Ret元件與Cdl元件分別代表SAM修飾層的緻密性與碳鏈數，Rs元件代表溶液電阻。將此電路模型評估SAM的特性可知：（1）SAM於金電極修飾時間約60分鐘即可達到飽和穩定的狀態。（2）SAM的碳鏈數越長，其電阻越大，而電容越小。（3）MUA溶液的飽和濃度為10 mM。（4）以dropping method進行SAM的修飾時，SAM的結構較使用immerse method所得到的更緻密，且修飾時間可由60分鐘縮短為20分鐘。（5）疏水性的SAM分子之緻密性較親水性的高。生物檢測應用上，△Ret與△Cdl對biotin的檢測線性範圍在2-10 μg/ml，但△Ret對biotin濃度的相關係數為0.9943，較△Cdl的0.9624為佳；Ret與Cdl的sensitivity分別為30.27 kΩ/μg/ml、3.49×10-5 nF-1/μg/ml，因此在biotin的檢測應用上，選擇相關性較佳的Ret作為biotin檢測的量化指標。
　　
　　探討實驗結果可知，電阻抗分析除了能夠評估SAM修飾層的特性外，對於avidin-biotin的檢測，已得到不錯的檢測範圍與再現性。故以研究中所建立之模擬電路與阻抗量測技術，可應用於biotin衍生物（如將biotin標定抗體、DNA等）或是其它親和性物質的檢測，進而發展一套生物感測技術。

　　By using self assembled monolayer (SAM) with different functional groups to modify a substrate, the surface of the substrate was suitable for specific bio-detection. The aim of this study were two, one was to characterize the physical properties of substrate with SAM modification, the other was that applied a layer of SAM coated with avidin protein on sensing electrode as a bio-probe to quantify the formation of avidin-biotin complex by impedance response in electrical impedance analysis.
　　
　　There were three types of SAM with carboxyl group to be coated on sensing electrodes by organic solvent which were DTBA, MUA and MHA. For making biotin probe, we use EDC/NHS reagent to activate the SAMs’ COOH to bind the avidins’ NH2 group. Circuit model is established by comparing with impedace response of DTBA, MUA and MHA after modification on the electrodes. In the circuit model, Ret and Cdl element represent density and chain length of SAM respectively. Rs element represents the resistance of supporting solution. Using circuit model to characterize SAM, we have several conclusions. (1) When modified time of SAM is about 60 minutes, SAM arives to saturate. (2) The longest SAM is increase in resistance and decrease in capacitance. (3) The saturated concentration of MUA solution is 10 mM. (4) Using dropping method, SAM becomes denser and modified time for SAM is reduced to 20 minutes as compared to immersion method. (5) Hydrophobic SAM is denser than hydrophilic SAM. For bio-detection, the linear range of biotin is 2-10 μg/ml bu means of △Ret and △Cdl. Correlation factor of Ret element (0.9943) is higher than that of Cdl (0.9624). Sensitivity of Ret and Cdl are 30.27 kΩ/μg/ml and 3.49×10-5 nF-1/μg/ml, respectively. Base on the findings above, we choose Ret element to the quantify concentration of biotin.
　　
　　In summary, EIS not only is used to characterize SAM modified electrode, but also provids good linear range and reproducibility to detection of avidin-biotin complex. To develop biosensing technique, simulation circuit and impedance analysis could be applied to detection of biotin derivative（such as biotin labled antibody or DNA）and affinity biosample.

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